|Publication number||US4658321 A|
|Application number||US 06/764,853|
|Publication date||Apr 14, 1987|
|Filing date||Aug 12, 1985|
|Priority date||Aug 13, 1984|
|Also published as||DE3467827D1, EP0171446A1, EP0171446B1|
|Publication number||06764853, 764853, US 4658321 A, US 4658321A, US-A-4658321, US4658321 A, US4658321A|
|Original Assignee||Siemens Aktiengesellschaft|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (5), Non-Patent Citations (2), Referenced by (22), Classifications (19), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This invention relates to a thermal overload protection apparatus for either a commutator or slipring motor.
One type of thermal overload protection is known from German published application No. 3,306,663 by Volkmar Koenig, published Feb. 2, 1984. In this known device used specifically to monitor the temperature of a hammer brush holder of an electrical motor, there is a thermal switch with a bimetallic or semiconductor element inserted in a side pocket-shaped seat of the brush mounting arm of a hammer brush holder, by which, in the event of excessive temperature rise and consequent exceeding of a specified temperature, a switch interrupts the electrical power supplied to the brush and thereby switches off the motor. It is desirable to provide a mechanism for thermal overload protection without the increase in cost and the decrease in reliability of having a thermally actuated electrical switch in series with the brushes.
The mechanism and application of the so-called form memory effect are known from existing applications (e.g., the journal "Material und Technik", 1978, No. 2, p. 59-65). Memory alloys are materials which after plastic deformation at low temperatures resume their original shape when heated above a critical temperature ("memory effect"). Memory elements having both a so-called one-way effect as welll as those with a so-called "two-way effect" are described in detail. With the one-way effect, the original shape is resumed only once when being heated, while with the two-way effect there is a reversible temperature-dependent form change behavior, wherein during the heating process the distortion is not reversed entirely and following subsequent cooling a form change toward the original distortion is attained. Both the one-way as well as the two-way effect can each be repeated as often as desirable.
By designing a brush holder in accordance with this invention it is possible to lift the brushes themselves, without additional power assistance means, from the surface of the commutator or the slipring suddenly and with great force and thereby to assure an interruption of the power circuit or switch off of the motor which is to be protected from excessive heatup. The expense for said overload protection can be further reduced for a hammer brush holder system of a commutator or a slipring motor by providing a memory element with a two-way effect. Special design, fabrication as well as manufacturing expense for additional bimetallic or semiconductor temperature switches and their mechanical mountings and electrical connections are thereby eliminated.
The object of this invention is to develop an overload protection which in contrast to the known device for temperature monitoring previously described, is easier to manufacture and install. A second object of this invention is to provide high operating reliability by maintaining a defined switch-off point when attaining or exceeding a preset temperature set value of the overload protection. A further object of this invention is to use the memory effect of certain alloys in the manufacture of cost effective, reliable thermal overload protection apparatus.
A thermal overload protection apparatus for brush electric motors, either of the commutator type contacts or of the slipring type contacts, is provided having a thermally actuated switching mechanism. A lever element, which is manufactured with a memory element, lifts one of the brushes from the rotating electrical contacts interrupting the power supplied, when the temperature of the memory element exceeds the set-value overload temperature.
In order to restrict as far as possible the required special alloy necessary for the switching elements, a further embodiment of the invention specifies that the lever element form a separate part of the brush support arm, whereby in the most practical fashion the lever element itself made of a memory element only forms the first part of the brush support arm, which is fixed-mounted in the brush support plate, while the remaining part of the brush support arm consists of an elastic spring element separately mounted to the first part, which presses against the surface of the commutator or the slipring via the brush mounted at its free end.
For the fabrication and manufacturing application of the model in accordance with the invention in an electrical motor with a tubular brush holder system with brushes aligned in the tubes largely radially to the commutator and pressed by a spring against its surface, one application of this invention fastens the lever element at one end to the exterior wall of the tube and has its other end bent directly or indirectly toward the brush in such a fashion that when exceeding the temperature set value, the free end moving contrary to the action of the spring is connected in either a directly contacting or a gear meshing fashion to the brush, thereby lifting it from the surface of the commutator. Two special embodiments of the application of the invention for a tubular brush holder system are further characterized by having the lever element connected to the brush in a lifting action from the surface of the commutator by either a torsional-swivel deflector or by a stretch-bend deflector.
While the specificaton concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention will be better understood from the following description of the four depicted embodiments taken in conjunction with the accompanying drawings in which:
FIG. 1 is an axial plan view on a first hammer brush holder system with one-piece brush support arms;
FIG. 2 is an axial plan view of a second hammer brush holder system with sectional brush support arms;
FIG. 3 is an axial plan view of a first tubular brush holder system with a torsional-swivel deflector lever element lifting the brushes;
FIG. 4 is an axial plan view of a second tubular brush holder system with a stretch-bend deflector lever element lifting the brushes.
FIG. 1 shows two one-piece brush support arms of a hammer brush holder system fixed-mounted to a schematically depicted brush support plate 16. The single-piece brush support arms made of a memory element having a two-way memory effect are shaped in the upper portion as the actual lever element 2 (memory element) and in their remaining portion as the spring-action element 21, in such a fashion that in normal operating condition the brushes 6 fastened to the lower free ends of the brush support arms are pressed against the surface of the commutator 1. The lever elements 2 made of a memory element with a two-way effect are designed so that when attaining or exceeding the temperature set value, for example a fixed temperature of 160 degrees Centigrade, a relatively expansive and temperature-independent lever action transpires practically instantaneously within a temperature range of 10 to 15 degrees Centigrade, whereby due to the large action capability of a lever elememt, the brushes 6 are moved into the position shown by the broken line and thereby lifted instantaneously from the surface of the commutator so that the power supplied to the commutator is interrupted. The brushes 6 remain in their lifted position until the temperature of the lever element made of a memory element cools down below the permissible temperature set value. The brush support arms then immediately resume their previous position and permit resumption of power supplied to the commutator.
FIG. 2 shows a variation of the design of FIG. 1 in which the lever element 3 made of a memory element with two-way effect is designed as a separate part of each brush support arm, to which a spring element 31 supporting the brush 7 at its lower free end is separately fastened. FIG. 2 also depicts the position by the broken line into which the brush support arm in the event of attaining or exceeding the temperature set value is instantaneously moved by the lever element made of a memory element, thereby simultaneously separating the power supply from commutator 1.
In FIG. 3 a further embodiment with a tubular brush holder system, is shown with the tube 10 fastened to a brush support plate 14, wherein a brush 8 is conducted and pressed against the surface of a commutator 1 by a brush pressure spring 11 bearing on its upper end. On the right side brush 8 is equipped with an impressed tooth grid 81 in such a fashion that a lever element 4 made of a memory element with two-way effect instantaneously moves the brush when attaining or exceeding the temperature set value by a torsional-swivel deflector from the position shown with the continuous lines into the position shown with the broken line, thereby mating with a corresponding tooth mesh 41 in the teeth of the tooth grid of brush 8; thereby, the brush is slightly lifted into the position shown in broken line, contrary to the pressure exerted by the brush pressure spring 11, so that the power supply between brush 8 and commutator 1 is again interrupted.
FIG. 4 shows another embodiment with a tubular brush holder system in accordance with the invention. This embodiment has the tubular brush holder system fastened to a brush support plate 15. In this case, when exceeding the temperature set value, the brush 9 aligned in tube 12 is lifted by the lever element 5 fastened to the end of the exterior wall of the tube facing the commutator 1 by a stretch-bend deflector at its other free end from the surface of the commutator; the total lever element, for that purpose, is initially bent away from the exterior wall of the tube above its fastening point at the exterior wall of the tube 12 in an area A in which it demonstrates marked memory characteristics and thereupon bent back in an area B characterized primarily by spring characteristics with its free end pressed against the external wall of tube 12 so that is free end when attaining or exceeding the temperature set value, due to the recoil of the lever element in area B, is pressed against brush 9, thereby lifting brush 9 from the surface of commutator 1 by a force component which acts against the spring power exerted by the brush pressure spring 13. For better mating of the end of the lever element pressing against brush 9 this end, in a fashion similar to the embodiment in accordance with FIG. 4, is designed with a ratched-like tooth grid 91, preferrably impressed, at least in the area of the free mating end. As is also seen in FIG. 4, tube 12 has an opening in the mating area of the free end of the lever element through which the free end of the lever element during a recoil motion of the lever element can pass in the event of excessive heatup of the commutator motor. If a memory element with a two-way effect is incorporated, then the free end of the lever element which lifts brush 9 from the surface of commutator 1, is retracted from the tooth grid 91 after the heatup to the temeperature set value recedes, and brush 9 is released so that it can once again be pressed down by the brush pressure spring 13 onto the surface of commutator 1, thereby releasing the power supply to the motor.
It will now be understood that there has been disclosed an improved thermal overload protection apparatus for electrical machines utilizing memory effect alloy elements. As will be evident from the foregoing description, certain aspects of the invention are not limited to the particular details of the examples illustrated, and it is therefore contemplated that other modifications or applications will occur to those skilled in the art. It is accordingly intended that the claims shall cover all such modifications and applications as do not depart from the true spirit and script of the invention.
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|US4034265 *||Feb 24, 1975||Jul 5, 1977||Essex International, Inc.||Electric motor protector|
|US4499517 *||Nov 14, 1983||Feb 12, 1985||Texas Instruments Incorporated||Motor protector particularly suited for use with compressor motors|
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|Citing Patent||Filing date||Publication date||Applicant||Title|
|US5053665 *||Aug 8, 1990||Oct 1, 1991||Asmo Co., Ltd.||Retaining structure of brush spring of electric motor|
|US5734219 *||Jun 17, 1996||Mar 31, 1998||Siemens Electric Limited||Sliding brush system with shape memory alloy element for two-speed direct current motor|
|US5975488 *||Oct 25, 1996||Nov 2, 1999||Mannesmann Rexroth Ag||Lifting magnet arrangement|
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|US8716618||Feb 19, 2008||May 6, 2014||Black & Decker Inc.||Angle grinder|
|US20050146239 *||Jan 21, 2003||Jul 7, 2005||Harald Kapitza||Brush holding plate for an electric motor, corresponding electric motor and assembly method|
|US20070013257 *||May 14, 2004||Jan 18, 2007||Bernhard Rupp||Brush arrangement for an electric machine|
|DE10342222A1 *||Sep 11, 2003||May 4, 2005||K Tec Kunststoffverarbeitung G||Pot/bowl-shaped support for carbon brushes in a servomotor has a bottom inner wall leading from the support's peripheral wall and interspersed by a commutator or shaft|
|EP1028500A2 *||Feb 10, 2000||Aug 16, 2000||Shop Vac Corporation||Thermal protection apparatus for electric motors|
|WO2002023682A1 *||Jul 6, 2001||Mar 21, 2002||Bosch Gmbh Robert||Brush holder for commutating machines|
|U.S. Classification||361/25, 310/68.00C, 310/249, 318/471, 310/238, 337/140|
|International Classification||H02K5/14, H02K11/00, H01R39/42, H02H7/08, H01H37/32, H02H7/085|
|Cooperative Classification||H02K5/148, H01H37/323, H01R39/42, H02K11/0047|
|European Classification||H01H37/32B, H01R39/42, H02K11/00F3|
|Aug 12, 1985||AS||Assignment|
Owner name: SIEMENS AKTIENGESELLSCHAFT, BERLIN AND MUNICH, GER
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:LINDNER, ADOLF;REEL/FRAME:004444/0340
Effective date: 19850719
|Nov 13, 1990||REMI||Maintenance fee reminder mailed|
|Apr 14, 1991||LAPS||Lapse for failure to pay maintenance fees|
|Jun 25, 1991||FP||Expired due to failure to pay maintenance fee|
Effective date: 19910414